Many different types of automated cartridge storage and handling systems have been developed to store cartridges at known locations, to retrieve the cartridges and transport them to a read/write device, and to return the cartridges to their assigned location in the system. Such data storage and handling systems are often referred to as “autochangers” or “juke box” data storage systems, particularly if they accommodate a large number of individual cartridges.
An autochanger storage system typically includes a cartridge storage rack or “magazine” as well as a read/write device to read data from, and write data to, the cartridges. The cartridge magazines provide storage locations for the cartridges and are commonly arranged so that they form one or more rows of vertical stacks. The cartridge read/write device may be located adjacent the cartridge stack, although the cartridge read/write device can be positioned at any convenient location. The data storage system also typically includes a cartridge access device for removing and inserting the cartridges in the magazines and read/write devices, and a positioning device to transport the access device among the rows and columns of cartridges.
When a host computer system issues a request for data contained on a particular cartridge, a control system associated with the storage system actuates the transport device to move the access device to the desired cartridge. The access device then removes the cartridge from the magazine and the transport device carries the cartridge to the read/write device. The access device inserts the selected cartridge into the read/write device so that the host computer may thereafter read data from, or write data to, the cartridge. After the read/write operation is complete, the access device removes the cartridge from the read/write device and returns it to a specified location in the system.
Although various operational modes are possible, storage systems commonly have the read/write device in a fixed location and use a moveable transport device to transport cartridges between storage racks or magazines and the read/write devices. The transport device is typically a robotic device which moves along a guideway in an X, Y, and/or rotary motion to access the various storage slots. The access device can have a plunge mechanism that engages a cartridge held within the read/write device or magazine and withdraws the cartridge.
Some data storage systems may be configured as scaleable, modular units in which multiple autochanger modules can be connected to incrementally expand the total system storage capacity. Each autochanger module can include a read/write device. In some configurations, multiple autochanger modules can be interconnected and use a single access device and transport device to move among the autochanger modules. In this manner, the access device assembly may access a cartridge from any autochanger module and access data from the cartridge from any read/write device in the stack of autochanger modules. Interconnected autochanger modules increase the total storage capacity and the total number of read/write devices that can be accessed simultaneously. A configuration of interconnected autochanger modules reduces cost since a single access device and transport device can be utilized to access the cartridges in each of the modules.
Often, one such storage system, also referred to as a library, has insufficient storage capacity, and therefore another library may be added to the system. The load balancing between libraries can be difficult, since, in many instances, it is necessary to move many of the data cartridges from one of the libraries to the other so that the workload may be balanced. The problem becomes more pronounced when still more libraries are added to the system. Conventional pass through systems for automated libraries typically require ports in adjacent library walls that allow a small number of data cartridges to be exchanged between the libraries via the access devices. The resulting configuration results in increased overhead for inventory tracking, as well as the number of other resources, such as access devices, that are required for each library.